A large variety of portable locks are available to reduce theft of objects. For example, bicycle locks can include a large metal chain or cable secured to a conventional pad lock. Unfortunately, the cable or chain of such locking systems is usually heavy and bulky, and they can be cut relatively easily with a pair of cable cutters.
An alternative bicycle lock includes a U-shaped shackle formed of cylindrical hard metal stock that locks to a cross-piece. An example of such a lock can be found in U.S. Pat. No. 4,155,231 to Zane et al. The U-shaped shackle can be mounted to a mount on a bicycle when not in use thereby facilitating its storage on the bicycle. But, the lock is heavy and not easily carried other than being stored on a bracket that travels with the object to be locked, so its use to lock objects other than bicycles is limited. Moreover, the U-shaped lock does not adjust in size for a particular locking application, such as to lock the bicycle to a tree or the like. Moreover, while the hard metal stock is more difficult to cut through than a traditional flexible cable or chain, it is still relatively easy to cut using conventional cutters.
More recently, efforts have been made to make a retractable cable lock that is compact and portable. An example of which can be found in U.S. Pat. No. 4,543,806 to Papandrea et al. A cable is coiled within a housing and retractable within the housing by a spring. The opposite end of the cable extends out of the housing and includes a locking structure that operably engages a lock mounted to the housing. A user can extend the cable from the housing to allow the lock to be wrapped around a tree or the like, but it is difficult to retract the cable back within the housing to tightly synch the cable to the item or items being locked. Moreover, in order to make the lock retractable, the cable must be thin. Such a thin cable can be easily cut with common cable cutters.